1. Field of the Invention
The present invention relates to an image pickup device and a camera equipped with a color filter for imaging color picture.
2. Related Background Art
A color image pickup device used in a color video camera, a color still camera and the like is disclosed in, for example, Japanese Patent Application Laid-Open No. H09-148549. A red, green and blue three-primary-color filters, a cyan and magenta complementary filters or others are formed on photoelectric conversion elements serving as photoelectric conversion units. Light passing through color filters is caused to be incident on the photoelectric conversion elements and is separated into an image signal of each color. A color signal can be obtained by synthesizing an image signal separated into each color. Such color filters formed on the photoelectric conversion elements are designated as “on-chip color filter”.
A general example of an image pickup device with a conventional on-chip color filter is described in detail with reference to the drawings.
FIG. 1 is a general cross section showing the structure of an image pickup device with an on-chip color filter. A photoelectric conversion unit 110 for generating signal charges according to the amount of incident light is formed on a semiconductor substrate 100. The photoelectric conversion units 110 are arranged in a lattice shape and provided for each of pixels.
A driving circuit (not shown) for creating a pixel signal corresponding to a signal charge generated by the photoelectric conversion unit 110 and transferring it to a horizontal scanning circuit in response to a controlling signal from a vertical scanning circuit provided around the photoelectric conversion unit 110 is provided on each pixel.
A gate electrode 109 of a transistor constituting the abovementioned driving circuit is formed on the silicon semiconductor substrate 100. A plurality of layers of wirings is formed thereon depending on a circuit configuration of the driving circuit. Incidentally, FIG. 1 shows an example of a configuration in which double layers of wirings are formed. An impurity diffusion region serving as a source and a drain of a transistor is formed on the semiconductor substrate 100.
Wirings 105 and 107 are patterned in a desired shape using aluminum and the like, and formed. The interlayer insulation films 106 and 108 consisting of, for example, SiO2 and the like insulate between the wirings 105 and 107 and between the gate electrodes. The topmost wiring layer 105 is insulated with a passivation film (not shown) made of, for example, SiN.
A first planarized film 104 made of, for example, acrylic resin is formed immediately on the passivation film. Color filters 103 corresponding to the pixels are provided on the first planarized film 104. Color filters 103 are formed by using, for example, photoresist containing pigments of the three primary colors: red, green and blue. The color filter is covered with any one of red, green or blue pigment for each pixel.
A second planarized film 102 with optical transparency is formed on the color filter 103. A microlens 101 for effectively converging incident light on the photoelectric conversion unit 110 is formed on the second planarized film 102. The microlens 101 is sometimes not disposed.
FIGS. 2A, 2B and 2C are cross sections showing a sequence for forming the conventional color filter described in FIG. 1.
When the color filter shown in FIG. 1 is formed, to begin with, the first planarized film 104 is formed on the surface of the passivation film (not shown). Thereafter, a negative color resist in which, for example, a green pigment is scattered is coated on the surface of the first planarized film 104. Subsequently, an ultraviolet ray of a wavelength of, for example, 365 nm is irradiated on a position where a green color filter is formed (hereinafter referred to as “filter G”) using a mask to develop a color resist. Thereby a filter G 103G is formed on the first planarized film 104 as shown in FIG. 2A.
In the next place, as shown in FIG. 2B, a negative color resist 103A in which, for example, a red pigment is scattered is coated on the entire surface of the first planarized film 104 so as to cover the filter G 103G. Subsequently, an ultraviolet ray of a wavelength of, for example, 365 nm is irradiated on a position where a red color filter is formed (hereinafter referred to as “filter R”) using a mask to develop a color resist, thereby forming a filter R 103R as shown in FIG. 2C.
Furthermore, a negative color resist in which, for example, a blue pigment is scattered (not shown) is coated on the entire surface of the first planarized film to cover the filters G and R. Thereafter, an ultraviolet ray is irradiated as is the case with the filters G and R to develop a color resist, thereby forming a blue color filter (hereinafter referred to as “filter B”).
As shown in FIGS. 2A, 2B and 2C, the second and following color filters to be formed are slightly elevated at the end portion of the pixels by the color filter previously formed. The color filter which is thus formed is formed substantially evenly in thickness inside the pixel.
FIGS. 3A and 3B are cross sections showing a sequence for forming a microlens illustrated in FIG. 1. When the microlens shown in FIG. 1 is formed, firstly, for example, a positive transparent resist is coated on the surface of the second planarized film 102. Secondary, an ultraviolet ray of a wavelength of, for example, 365 nm is irradiated to develop the transparent resist using a mask on which light shielding portions are formed except for the boundaries between the pixels. Thus, a rectangular-parallelepiped structure 101A is formed as shown in FIG. 3A. Thereafter, the rectangular-parallelepiped structure 101A is thermally fused to form a microlens 101 as shown in FIG. 3B.
A configuration on a color filter is disclosed in Japanese Patent Application Laid-Open No. 2000-012814, in which microlenses in a color image pickup device equipped with microlenses are formed to be equal in curvature and thickness for each pixel, and the three-primary-color thin filters are provided on the surface thereof, thereby enabling providing a high color reproduction.
On the other hand, Japanese Patent Application Laid-Open No. 2004-281911 has disclosed a configuration on an on-chip color filter formed to be embedded between wiring layers in an image pickup device with multi-layered wirings. Such a configuration suppresses eclipse of an oblique incident light caused by a wiring layer to improve sensitivity shading, dependence of sensitivity on F-number and color mixture. FIG. 4 shows a regular octagon microlens as one example of a microlens. A gap between adjacent microlenses is designated as a “microlens gap 101B”. It is desired that the microlens gap 101B is formed as narrowly as possible to improve sensitivity in a sensor and to suppress a color mixture.
The microlens gap 101B, however, is larger in the direction of 45 degrees than in the parallel direction with respect to a pixel arrangement direction. Even though the microlens gap in the parallel direction with respect to the pixel arrangement direction is reduced close to zero, it is technically difficult to reduce the microlens gap in the direction of 45 degrees with respect to the pixel arrangement direction.
The following is a description of color mixture.
Light beams “a” and “b” are incident on an image pickup device, for instance, through optical paths shown in FIG. 5. The light beam “a” passed through a microlens 101, a second planarized film 102, color filter 103, a first planarized film 104. Further it is transmitted through a plurality of interlayer insulation films 106 and 108 and reaches the photoelectric conversion unit 110.
The light beam “b,” on the other hand, is incident on the boundary between the pixels, that is, the gap between the adjacent microlenses. The light beam repeats reflections, scattering, refraction, and diffraction at the boundary between the adjacent color filters and in the wiring layers 107 and 105, straying, and in part reaching the photoelectric conversion unit. Even in a case where the microlenses are not provided, light beams incident on the boundaries between the pixels stray similarly.
Stray light components sometimes cause a problem with color mixture because of their reaching the photoelectric conversion units of pixels which stray light components should not reach. The major part of the stray light components are transmitted through the boundaries between the color filters of the adjacent pixels, and reflected by the wiring layers. These components will be transmitted through any of the color filters if there are no boundaries between adjacent color filters. When the incident light is white light, its components reflected by the wiring layers are attenuated to at least about one third by transmitting them through the color filters. Therefore, in order to reduce the stay light components it is important to transmit light beams through the color filters with the gaps lessened between adjacent color filters.
For example, when light beams from a red subject are incident on a blue pixel, most of light beams incident on the microlens are absorbed by the filter B. However, stray light components incident on gaps between adjacent microlenses are incident both on the filter B and on the filter G formed next to the former. These components incident on the filter G are incompletely absorbed, and partly transmitted. Thereafter, the components repeat reflections, scattering, refraction, and diffraction and partly reaching the photoelectric conversion unit of a blue pixel. Color mixture is thus caused by information from a red subject reaching the photoelectric conversion unit of a blue pixel which it should not reach. As described above, to decrease a color mixture it is important to reduce the amount of light transmitted through color filters at the boundaries between pixels.
In the configuration described in the aforementioned patent publication, however, the amount of light transmitted through color filters at the boundaries between pixels is not decreased, so that color mixture is liable to be caused by light beams being transmitted through gaps between microlenses or through adjacent incorrect color filters and being incident on the photoelectric conversion unit.